The overall objective of our research is to determine how the mammalian brain stem functions to integrate sensory inputs with the on-going central respiratory rhythm to produce a respiratory motor response. Our research is directed at understanding the function of the dorsal respiratory group (DRG) within the medullary ventrolateral solitary nucleus of cat. This concentration of respiratory neurons is the likely site where pulmonary receptor inputs are incorporated into a respiratory motor response. These inputs have profound effects on respiratory cycle timing and the pattern of respiratory activity. We propose to study these cells by two different approaches. First we will directly test the hypothesis that different types of pulmonary receptor afferents make monosynaptic connections with different types of DRG neurons. To do this we shall utilize the technique of spike triggered averaging to determine the explicit connectivity between pulmonary afferents and DRG neurons whose membrane potentials are recorded intracellularly. We shall also determine the central projections of single pulmonary afferents using this technique by averaging medullary extracellular field potentials. In these studies we shall use as triggers extracellularly recorded spikes from single nodose ganglion cells. These are recorded with ease using a special "floating" type tungsten microelectrode. Second, we will test the hypothesis that different types of DRG neurons have unique morphologic structures. Morphologic structure will be directly related to the neurophysiologic properties of single neurons. To do this we shall intracellularly inject the marker horseradish peroxidase into characterized DRG neurons. Following standard histochemical procedures we shall serially reconstruct these neurons to determine morphologic characteristics such as somal size and shape, dendritic structure and extent, axonal projection, and collateralization. These results will provide us with a clearer understanding of the structure and function of this important collection of medullary respiratory neurons.